Optical apparatus for measuring by deflection



April 8, 1952 M. F. B. PICARD ETAL 2,592,329

OPTICAL APPARATUS FOR IUEASUFIIG BY DEFLECTION Filed Aug. 9, 1946 @Usi MMM@

da ATTORNEYS Patented Apr. 8, 1952 Maxime .Felix Benoit Picard.andtMarcelxSchlume berger,L Paris, France, assignqrsgito ,SoieteeA4 ProspectiomElectrique PrdcedesSchlumhergen Paris, France, as corporation. aggirano@ 4 Apunta-.annum 9. 194e--ser1s1No= 68ans.:

' .Immense August 2349451;

0,111: invention .has .for itsobiect improvements. in apparatuses for the measurement by deectionf such ,as galvanometers etc. comprising a revolving mirroror any, other `equivalent optical device that` projectsa pencil of rays on .avgraduated scale, a.

dial, aA paper .or sensitive ,film for the, purpose of recording on charts, eige-in,whichth eopticalr device is immersed in a liquid.`

In apparatuses of this kindnthe optical `device is, .enc1osed ,wthn a container lledwithpliquid,

and thepencil of raysemployedtravels fromthe,

outside to, the ,inside of thiscontainer and vice versa through a ,.closed aperture by meansY of a..

transparent sheet, .thatis madegenerally of glass. As' the-liquidflling the container has an index of refraction v,differing from that, of air, great trouble is ,experienced in securing on the scala, dial or sensitivelm va sharp lightspot providingv a denite Vreading or possibly thesuitablewrecording of achart. If it is assumed, in fact, that the optical revolvingdeviceisnarroweddown to aV iiat mirror integral with the ,movable gear of the` apparatus andv that the apertureof the Acontainer striking on theinteriori Vthe vsystem will emerge from it with. an increasing dispersion ,when Y the deviationfrom the.,mirror. becomes arcata?,Y and will exhibit on the sensitive ablurredlightsv spot, that 1s-v unrelialme for.recorclina 'rhegtrour ble increases, moreover, IromtheV iactlgthat the.

refractive, index of, the., liquid, in wliicl'iftlifi s ref v olving index isI immersed, variesl ,considerably as a-generai rule ,withcthe temperatureso muchgflso that an optical SySemthat-givesgoodrea ings at a-,certain `temperature may develop ineicactitude .at.anotherqtemperatura .This is af series drawback especiallywhen it isdesiredmto record with instruments, that are-,designed f orfezmployment, elsewhereV thanfin a laboratory asis espe? cially the case:for.,geophysicalapparatuses etc,

The present yinvention.aimsat aY cure Vfor this drawback and;4 for4 the. Vper-ff,ectiorrof rvoptical, de vices that en' surejirr everylrcircumstanceand within -veryf wide/frangess ot temperature, inside which it desired to workltlgle-l apparatus; (includedfor instancerbetweenT2090. and +60L7 0,., ashappensforfinstruments@employed e. a in geophysics) :the projectionl -ofV a light-spot rgiving especially-afperfectlysharp record. To thisfend, thedevicesV employed :in accordance lwith the inf vention-maycompriselone:ermorefofrthefollowinsefvesturesz;

2.. Y a; 'I-ha-SQParatinsaQIate between. the-liquid in which: tbetmirror or; othervequivalent device; is

innnersed,,andv thevfree atmosphere will,` assume prerably theshape-,of a-,hollowvspherical memf berthatsis vcenterednat, the -yeryleast closely on` the centralpoint of` thefmirror, in suchaway that thein cident lrays `that-strike .the mirror and are ree ctel by1the mirrorcrossthe two surfaces of the platefinwa substantially,perpendicular course. thus-,cutting out the prism eiiect.

b.. Inordenthattheoptical systemV made up of the mirror, the; liquid ;in which it: is l immersed and; the-.free atmospherefmay vnot have too great.

a,-.p ower, ,the mirrorgwill bepreferably convex,

insteadyof beingfl at,and its ,curvature will be iiguredin such ac-waythatthefocal length of the assembly has anappropriate value.

c.-,In frontgof the-reflecting member, such as a mirror-:or the-like means. is arranged-alens of given power and made of ag lass,with a suitable refractivey indexand of. whichV the characteristics willbe=selected as a functionof thezother charac teristics of the optical system, in sucha manner that .theitotal powerof theassembly maybe practically.- independent of` the.` temperature, which condition may be obtained in practice as applicant4 unit in accordance withv the :invention andthisv unit 4will consistent., a lens-.with asilvered back.

d. 'I'he transparentplate dividing-y the liquid fromvthe .atmaschere..` instead Ofbeln'g "formed lby assimplethinwall may bemade up of ,a comparatively thick platebounded by twoV surfaces that areconcentric with thecentral point ofthe spherical mirror,y and` the thickness of which `will be calculatedso as tQicut outchromatc aberration orchromatisnfi.ontheaxis.V

Otherpbiets v.and.feat,urnstitheinvention .will maltel v their appearance throughout the descriptionvgiven below inthe accompanying drawing that deals with aspecial method `l0f carrying l intoV eiect the lpresent ,invention4 In the drawing, a diagrammatic section is shown of an. optical .devicseinaccordance with the invention. In the drawing, Ifdenotes the mirror that.v is, incorporated with. the movab1e partv of any., suitable A, measuring apparatus I 0 onl which mirror a pencil of light originating from alight sourceSimpinges; the mirror reectsthepencil ontaafphotographic; lm y P` that movesin a suitable way `so as to .allow a.,.;continuous xrecord of the deviations-of themovable. parts of the `meas-y uringl apparatus;` Thedightfsource as `wellgas the photographic lin, maiybeicnnedandarf l ranged in any suitable way in accordance with customary methods; the shape and arrangement of these members does not come into consideration as far as the present application is concerned.

In line with the invention, the mirror l is formed by the back silvered surface of a lens 2 of which the outer surface is shown at 3. The curvatures of the faces I and 3 of-the lens will be selected as will be explained later in accordance with the invention.

The reflecting assembly is immersed in a liquid 4 that is divided from the atmosphere by a plate 5 that has, in accordance with the invention. a certain thickness and of which the surfaces separating it from the liquid 4, on the one hand, and from the outside atmosphere, on the other hand, are formed respectively by spherical surfaces 6 and l centered on the central point of the mirror I.

A calculation may be made as follows of the various members of this optical device in order to secure the projection of a sharp light-spot on the fllm P in all circumstances and especially under any variations of temperature to which the assembly may be subjected.

In order to take into account these variations of temperature that cause, as stated above, a

variation in the refractive index nl of the liquidv 4, the following operation will be carried out:

In calculating the power ff) of the optical assembly it will be observed that this power is a function f depending especially on the refractive index n4. It will be supposed then that the derivative of this function in relation to the index nl, for the value of this index corresponding to an average suitablyl selected temperature, C. for instance, is zero, that will give a primary relationship between the different elements of the optical system;

If n2 is called the refractive indexof the lens 2, R the radius of the surface I, R3 the radius of the surface 3, Re the radius of the surface 5 and R7 the radius of the surface 1 and pi, pa. ps, and p7 the reciprocals of the radii, this relationship will be written:

Moreover, the vchromatic aberration may be corrected in the following manner:

The power 1 of the optical assemblyythe other data remaining unaltered, is a function of the refractive indices 11g-ns of the lens 2 and the plate 5, that vary with the wave length of the light radiation employed. It is noted then, in regarding now n2 and 11.5 as independent variables, that the total differential of I is zero, supposing the differentials of the refractive indices nz and 11.5 give out the dispersion of the corresponding glasses between two given spectrumlines (lines F and G for instance).

Thisleads to the second relationship:

Anf, and Am being respectively the dispersion of the glasses forming the lens 2 and the enclosing glass 5.

By placing on i1 a given value to ensure the optical operation contemplated and settling the value of R1 consistent with the possible dimensions of the arrangement two other equations are obtained that with the two equations given above completely denne the system.

Numerical exampZe.-Suppose for instance it is desired to execute a system of a power b of 4 dioptres with R1=50 mm., and p7=20 dioptres.

The index of refraction of the liquid will be taken equal to 1.5.

The glass of the mirror is for instance a barium crown with index 1.6 and its dispersion between the lines F and G is 0.006.

The enclosing glass is an extra dense flint with an index 1.75 and a dispersion=0.015.

The the following values are found:

76:22.472 mm. ra=19.417 mm. 1'1='153.85 mm.

It will be observed that, in this calculation, only the thickness of the mirror has been omitted. This thickness may be very slight. for the dimensions of the mirror are always small; it is possible then to include it in the calculation of the focal line and to make the corrections on standard lines.

Obviously, numerous modifications can be introduced to the devices described without widening the scope of our invention that is not tied down in any way to the examples submitted for carrying the invention into effect.

What we claim is:

l. In an apparatus for optically measuring dei'lections, the combination of a pivoting member subjected to deflection, a reflecting surface rigid therewith, a source of light illuminating said refleeting surface, a hollow vessel enclosing said pivoting member, said vessel having a transparent spherical portion through which light may be transmitted from said source to said reflecting surface, said transparent spherical portion having concentric front and rear surfaces with centers of curvature located substantially at the pivoting point of the pivoting member, a refracting liquid in said vessel, said liquid having an index of refraction greater than one and extending' to a level above said reflecting surface, and means outside of said vessel and in the path of the light reflected from the reflecting surface through said transparent spherical portion for providing measurements of said deflections.

2. In an apparatus for optically measuring deflections, the combination of a pivoting member subjected to deflection, a convex mirror rigid therewith, a source of light illuminating said convex mirror, a hollow transparent vessel enclosing said pivoting member, said vessel having a spherical portion through which light may be transmitted from said source to said convex mirror, said transparent spherical portion having concentric front and rearsurfaces with centers of curvature located substantially at the pivoting point of the'pivoting member, a refracting liquid in said; vessel, said liquid having an index of refraction greater than one and extending to a level above said convex mirror, and means outside of said vessel and in the path of the light reflected from the convex mirror through said transparent spherical portion for providing measurements 0f said deflections.

3. In an apparatus for optically measuring delections, the combination of a pivoting member subjected to deflection, a reflecting surface rigid therewith, a, source of light illuminating said refleeting surface, a hollow transparent vessel enclosing said pivoting member, said vessel having a spherical portion through which light may be transmitted from said source to said reflecting surface, said transparent spherical portion havper-:44.5 dioptres p3=51.5 dioptres pi=6.5 dioptres ing concentric front and rear surfaces with centers of curvature located substantially at the pivoting point of the pivoting member, a refracting liquid in said vessel, said liquid having an index of refraction greater than one and extending to a level above said reflecting surface, a lens of predetermined power and refraction index inside the liquid and interposed between the reflecting surface and the transparent vessel and shaped so as to provide a total power which is independent of the variations of the refraction indices with varying temperatures, and means in the path of light reflected from the reflecting surface through said transparent spherical portion for providing measurements of said defiections. p

4. In an apparatus for optically measuring deections, the combination of a pivoting member subjected to deflection, a lens with a rear refleeting surface rigid therewith, a source of light illuminating said reflecting surface through the lens, a hollow transparent vessel enclosing said pivoting member, said vessel having a spherical portion through which light may be transmitted from said source to said reflecting surface, said transparent spherical portion having concentric front and rear surfaces with centers of curvature located substantially at the pivoting point of the pivoting member, a refracting liquid in said vessel, said liquid having an index of re fractiongreater than one and extending to a level above said reflecting surface, and means outside of said vessel and in the path of the light reflected from the reflecting surface through said transparent spherical portion for providing measurements of said deflections.

5. In an apparatus for optically measuring deilections, the combination of a pivoting member subjected to deflection, a reecting surface rigid therewith, a source of light illuminating said reflecting surface, a hollow transparent vessel enclosing said pivoting member, said vessel having a spherical portion through which light may be transmitted from said source to said reflecting surface, said transparent spherical portion having concentric front and rear surfaces with centers of curvature located substantially at the pivoting point of the pivoting member so as substantially to eliminate position chromatism, a refracting liquid in said vessel, said liquid having an index of refraction greater than one and extending to :a level above said reflecting surface, and means outside of the vessel and in the path of the light reflected from the reflecting surface through said transparent spherical portion for f providing measurements of said deflections.

6. In an apparatus for optically measuring deflections, the combination of a pivoting member subjected to deflection, a lens with a rear reflecting surface rigid therewith, a source of light i1- luminating said reflecting surface, a hollow transparent vessel enclosing said pivoting member, said vessel having a spherical portion through which light may be transmitted from said source to said reflecting surface, said transparent spherical portion having concentric front and rear surfaces lwith centers of curvature located substantially at the pivoting point of the pivoting member, a refracting liquid in said vessel, said liquid having an index of refraction greater than one and extending to a level above said reflecting surface, the lens and vessel wall being shaped so as to provide a total optic power independent of the variations of the refraction indices with varying temperatures, and means outside of the vessel and in the path of the light reflected from the reflecting surface through said transparent spherical portion for providing measurements of said deflections.

7. In optical apparatus for providing indications of deflections, the combination of a vessel provided with a spherical, transparent portion having concentric front and rear surfaces and containing a refracting liquid having an index of refraction greater than one, a reflecting member pivotally mounted in Said vessel substantially at the center of curvature of the front and rear surfaces of said transparent spherical portion and submerged in said liquid. said reflecting member being rotatable in accordance with a deflection, a source of light disposed so as to i1- luminate said reflecting member through said transparent spherical portion, and means external of said vessel and in the path of light reflected from said reflecting member for providing indications of displacements of said reflected light.

MAXHVIE FELIX BENOIT PICARD. MARCEL SCHLUMBERGER.

REFERENCES CITED The following references are of record in the file of Vthis patent:

UNITED STATES PATENTS Number Name Date 1,098,905 Jacob et al June 2, 1914 1,520,245 Humbrecht Dec. 23, 1924 1,871,380 Legg Aug. '9, 1932 1,960,169 Schoenberg May 22, 1934 1,982,333 Thomander i Nov. 27, 1934 2,019,871 Pettingill et al. Nov. 5, 1935 2,295,802 Nicoll Sept. 15, 1942 2,384,540 Flint Sept. 11, 1945 2,428,369 Kammer Oct. 7, 1947 

